Diseases of the retina and vitreous body are the principle causes of blindness, and among them are outstanding diabetic retinopathy and age-related macular degeneration.
Although there are references in the prior art of the potential use of somatostatin and analogues in the treatment of posterior segment eye diseases, based on the evidence of the overexpression of somatostatin receptors in these disorders, there are no clear examples of therapeutic effect.
The presence of endogenous somatostatin and somatostatin receptors in the different parts of the human eye has recently been described. Therefore, for example, the somatostatin receptors sstr1, sstr2 and sstr5 have been detected in the lacrimal glands, conjunctiva, cornea and nasolacrimal ducts [Minsel et al., Endocrinology, 2009, 150(5): 2254-2263]. In the posterior segment of the eye the presence of genes corresponding to the somatostatin receptors sstr1, sstr2, sstr3, sstr4 and sstr5 in the retina, ciliary body and choroids in healthy human eyes have been described [Klisovic et al., Investigative Ophthalmology & Visual Science, 2001, 42(10): 2193-2201], the presence of sstr2 and sstr3 mRNA in the retina [van Hagen et al., European Journal of Endocrinology, 2000, 143: S43-S51; Cervia et al., Molecular and Cellular Endocrinology, 2008, 286: 112-122] and also the presence of endogenous somatostatin in the vitreous humor and the retina [Simó et al., Diabetes Care, 2002, 25(12): 2282-2286]. It is also known in the prior art that there is a lower expression of somatostatin in the retina in the first phases of diabetic retinopathy, possibly associated to retinal neurodegeneration [Carrasco et al., Diabetes Care, 2007, 30(11): 1-7].
There are different routes of administration of drugs for the treatment of posterior segment eye diseases such as systemic, topical, intraocular and periocular administration.
Document WO 02/09739 A1 describes the use of somatostatin or an analogue thereof for the treatment or prevention of ocular disorders. Among the routes of administration named in this document, the preferred route is systemic parenteral administration, subcutaneous or intramuscular, and there is no indication in said document of a formulation in the form of eye-drops for the administration of somatostatin or an analogue of it. However, in the case of systemic administration it is difficult to reach therapeutic concentrations in the posterior segment of the eye due to the hemato-retinal barrier, which limits the penetration of medication into the eye. Another general disadvantage of systemic administration is that its effect is not local and it is not directed exclusively to the posterior segment of the eye. Furthermore, in the case of somatostatin, high doses would be necessary due to its instability in blood. In the case of the analogue octreotide, different clinical studies have assessed its effects through systemic subcutaneous administration, even if the results do not show a clear therapeutic effect [Wegewitz et al., Current Pharmaceutical Design, 2005, 11: 2311-2330; Palif et al., Investigative Ophthalmology & Visual Science, 2008, 49(11): 5094-5102].
An alternative to the low availability of the systemic route of administration in the posterior segment of the eye is the local administration in the posterior segment of the eye through intraocular injections and periocular injections such as subconjunctival, sub-Tenon and retrobulbar injections, or subconjunctival implants in this segment [Geroski et al., Investigative Ophthalmology & Visual Science, 2000, 41(5): 961-964; Kiagiadaki et al. Investigative Ophthalmology & Visual Science, 2008, 49(7): 3080-3089]. However, these forms of administration are not comfortable for the patient and present secondary effects whose frequency increases if they are carried out repeatedly. Furthermore, in the case of implants, they entail a surgical intervention. Although these type of treatments have shown to be effective in preclinical studies, they require the regular application of injections which in some cases have secondary effects such as retinal detachment, cataracts, rubeosis or endophthalmitis [Geroski et al., Investigative Ophthalmology & Visual Science, 2000, 41(5): 961-964; Herrero-Vanrell et al, Journal of Drug Delivery Science and Technology, 2007, 17(1): 11-17; Robertson et al., Journal of Ocular Pharmacology and Therapeutics, 1997, 13(2): 171-177].
Another alternative to the previous routes of administration of drugs to the eye is topical ocular administration. However, the topical ocular channel, as a route of administration of medication whose target is in the posterior segment of the eye, has been limited up until now due to the estimation that the percentage of active substance capable of reaching the posterior segment is insignificant in the majority of cases. [Andrés-Guerrero et al., Archivos de la Sociedad Española de Oftalmologia, 2008, 83: 683-686].
Within the prior art several options for topical ocular administration of somatostatin and analogues have been mentioned. Therefore, for example, document US 2005/074497 A1 describes a hydrogel which contains an anti-angiogenic drug, such as octreotide, for the treatment of posterior segment eye disease. Octreotide is disclosed in this patent application inside of a vast list of drugs. Furthermore, no example of octreotide or any other drug is described in this document. The hydrogel is placed in contact with the eye by using a contact lens or alternatively it is attached to the eye using adhesives or by surgical intervention. Administration by eye drops is explicitly excluded in this document. However, administration using a contact lens entails the risk of the eye becoming infected by pathogens and additionally, it is not tolerated by patients with increased intraocular pressure.
Another possibility is topical administration in the form of an ointment or unguent in the inner part of the eyelid. However, ointments tend to be uncomfortable and lower visual acuity due to their excessive viscosity and slow absorption.
Document WO 99/24019 A1 also describes a dry, solid formulation made of different drugs, among them somatostatin, which is reconstituted in a liquid solution and is administered as ophthalmic drops. Although this document does not provide any example of a formulation of somatostatin, nor any indication of this or another drug which reaches the posterior segment of the eye applied using eye drops.
On the other hand, document U.S. Pat. No. 5,182,258 A describes a formulation in the form of eye drops which, through the nasolacrimal system, is used for systemic administration, where the active principle being administered can be somatostatin, among many others. However, nothing is said in this document about the administration of this or another active principle for the treatment of posterior segment eye disease. The same occurs for other formulations in the prior art where octreotide is administered by topical route without a possible application for the treatment and/or prevention of posterior segment eye diseases being indicated [Danesi et al., Clinical Cancer Research, 1997, 3: 265-272; Demir et al. Documenta Ophthalmologica, 2003, 107: 87-92].
Therefore, there is in the prior art the need to find a form of topical ocular administration of somatostatin or an analogue thereof for the local treatment and/or prevention of posterior segment eye diseases which resolves both the problems of comfort for the patient and low therapeutic availability in a pharmaceutically acceptable formulation.
The object of this invention is a topical ophthalmic composition, a liquid pharmaceutical formulation which is administered topically in the eye, of somatostatin or an analogue thereof, which reaches the posterior segment of the eye, joins the somatostatin receptors present there and which is applied for the treatment and/or prevention of posterior segment eye diseases which benefit from the binding of somatostatin or its analogues to the somatostatin receptors. This invention provides an unprecedented breakthrough in the topical ophthalmic administration of peptides, and particularly, somatostatin or its analogues.